1. Field of the Invention
The present invention relates to a buckle device for use in a vehicle seat belt system and into which a tongue plate is inserted for engagement therewith.
2. Description of the Related Art
Among buckle devices used in seat belt systems, a buckle device having a so-called direct locking mechanism is known in which a lock member is held in a locked state by a release button disposed slidably in the direction of insertion and withdrawal of the tongue plate. The locked state of the tongue plate is canceled by operating the release button by pressing the same.
With this buckle device, however, when inertial force has acts in the direction in which the release button is operated, there is a possibility that the release button moves due to the inertial force, thereby canceling the locked state of the tongue plate. That is, there are two cases where the inertial force acts in the direction in which the release button is operated: (1) those attributable to vehicle vibrations when running on a rough road and (2) those in which a support member for supporting the buckle device on the chassis absorbs energy caused by plastic deformation.
In the latter case, the support member undergoes plastic deformation due to a large load acting on the support member, with the result that the overall buckle device moves suddenly in the direction in which the tongue plate is pulled, and the release button moves in the direction in which it is operated for release, by the inertia of the release button. Specifically in cases where the support member is constituted by material such as a webbing and is secured by being wound around an anchor provided on the chassis, and a portion of the webbing adjacent to the wound portion has been sewn in a folded state, the sewn portion is adapted to be cut off so as to absorb the energy when a large load occurs. In this case, there is a possibility that when the webbing is drawn out suddenly due to the cutting off of the sewn portion upon absorbing the energy, the release button moves in the direction in which it is operated for release, owing to the inertial force.
In addition, among buckle devices used in seat belt systems, one having a so called indirect locking mechanism is known in which the lock member is held in a locking state by means of a lock assisting member such as a pin. When the release button is operated by being pressed, this lock assisting member is adapted to move so as to cancel the locked state of the tongue plate.
With this type of buckle device as well, an inertial force acts in the direction in which the release button is operated, so that when the release button moves due to this inertial force, there is a possibility that the locked state of the tongue plate is canceled.